Early '99: A Record Tornado Season?

By
Laureen Chambliss, weather.com

The Weather Channel

Tornadoes are one of the most violent and deadly forces of nature. They can
strike suddenly and devastate an entire community within minutes.

Before the height of severe weather season had even arrived, 1999 had become
a record setting year for tornadoes. In January, a month better known for
blizzards and ice storms, a staggering 169 twisters occurred.

The Southeast received the lion's share. On the 17th, nine people were killed
as tornadoes raged across Arkansas, Missouri and Tennessee. Over a three day
period beginning on January 21, 104 tornadoes touched down from Arkansas to
Florida. One of those tornadoes ravaged Clarksville, Tennessee. More than two
dozen buildings were leveled in the downtown area. Incredibly, there were no
deaths and only a few injuries.

By month's end, 19 people had fallen victim to tornadoes in the United
States. January's preliminary total of 169 tornadoes more than triples the
previous record of 52 set in 1975.

"Tornadoes during January are not unprecedented," said Stu Ostro, Meteorology
Team Leader at The Weather Channel. "What was unusual about the recent outbreaks
was the magnitude of the outbreaks, we're talking scores of tornadoes, also the
area that was affected was a bit farther north than what would typically be the
case in the middle of the winter."

Tornadoes are more likely to strike along the Gulf Coast during the winter.
While the number of tornadoes was unusually high this winter, the weather events
leading up to them were not necessarily out of the ordinary.

"We've had disturbances coming across the southern part of the U.S. which
have resulted in a triggering of thunderstorms with a strong vertical wind shear
that we've associated with these disturbances this time of the year. And with
the relatively warm, moist air coming up from the Gulf of Mexico the stage had
been set a number of times for a lot of tornadoes," said Howard Bluestein,
Professor of Meteorology at the University of Oklahoma.

But were those tornado producing weather systems prompted by something
greater? La Niña's influence has not been ruled out.

"That's an area thats under a lot of research, how El Niño and La Niña
project on extreme weather events," said Antonino Busalacchi, NASA Research
Oceanographer, "During La Niña what we have the tendency for, is for these
collisions of air masses; dry cold air from the north colliding with moist warm
air from the south. When that happens it sort of sets the stage for more
tornadoes, but doesn't necessarily mean we can predict exactly or precisely that
there are going to be more in a certain region of the country."

"We do think that the recent El Niño and now La Niña have contributed to the
locations in which the tornado outbreaks have occurred," says Ostro, "However,
tornado formation is a very complex process and by no means have El Niño and La
Niña solely determined which communities have been hit."

Forecasters do agree that La Niña makes U.S. weather more variable; however,
they can't say if there will be more extreme tornado outbreaks during the
remainder of 1999.